Electrolyte solution, and electrochemical device and secondary battery using same

Abstract

Provided are an electrolyte solution capable of improving the durability of an electrochemical device, reducing the amount of gas generation, and reducing the amount of metal deposition, and an electrochemical device and a secondary battery using the same. An electrolyte solution containing at least one compound represented by general formula (1). Rf1OR (1) (Rf1 is a fluoroalkyl group having 1-5 carbon atoms, and R is K or Na).

Description

Technical Field

[0001] The present invention relates to an electrolyte, an electrochemical device using the same, and a secondary battery. Background Art

[0002] With the recent trend of weight reduction and miniaturization of electrical products, the demand for electrochemical devices such as secondary batteries has increased rapidly. Furthermore, by making electrical products more high-performance and endowing them with functions that they did not have hitherto, the demand for electrochemical devices that can withstand use for longer periods and under severe conditions has been continuously increasing.

[0003] It has been proposed that by containing a specific additive, even when an electrochemical device such as a lithium-ion secondary battery is stored at a high temperature, the capacity retention rate is high, dissolution from the positive electrode is suppressed, and an electrolyte solution that hardly generates gas is obtained (Patent Document 1).

[0004] In addition, research has been conducted on sodium-ion secondary batteries that use sodium ions as charge carriers. Since sodium is more abundant than lithium and can be obtained at low cost, it has attracted attention as a low-cost and large-scale secondary battery. As an electrolyte suitable for a sodium-ion secondary battery, for example, a non-aqueous electrolyte for a sodium-ion secondary battery containing a boron compound having a specific structure has been proposed (Patent Document 2). In addition, a non-aqueous electrolyte for a sodium-ion secondary battery containing dioxathiolane having a specific structure has been proposed (Patent Document 3).

[0005] Prior Art Documents Patent Documents Patent Document 1: WO 2019 / 003780 Patent Document 2: JP-A-2016-85890 Patent Document 3: JP-A-2019-46614 Summary of the Invention

[0006] Technical Problem to be Solved by the Invention An object of the present invention is to provide an electrolyte that can improve the durability of an electrochemical device, reduce the amount of gas generated, and reduce the amount of metal precipitation, an electrochemical device using the same, and a secondary battery.

[0007] Technical Means for Solving the Technical Problem The present invention is an electrolyte containing at least one compound represented by the following general formula (1).

[0008] Rf 1 OR (1) (Rf 1 is a fluoroalkyl group having 1 to 5 carbon atoms. R is Na or K.) The Rf of the compound represented by the above general formula (1) 1 is preferably any one of the following formulas (1a) to (1e).

[0009] (1a)CF2HCF2 (1b)CF2HCF2CH2 (1c)CF3CHFCF2 (1d)CF3CF2CH2 (1e)CF2HCF2CF2CF2CH2 The content of the compound represented by the above general formula (1) is preferably 0.01 to 10000 ppm with respect to the entire electrolyte.

[0010] It is further preferred to contain a compound represented by the following general formula (2).

[0011] Rf 2 ORf 3 (2) (Rf 2 、Rf 3 are independently fluoroalkyl groups having 1 to 4 carbon atoms.) The compound represented by the above general formula (2) is preferably at least one selected from CF2HCF2CH2OCF2CF2H, CF2HCF2CH2OCF2CHFCF3, and CF3CF2CH2OCF2CF2H.

[0012] The content of the compound represented by the above general formula (2) is preferably 0.1 to 90% by mass with respect to the entire electrolyte.

[0013] The content of the compound represented by the above general formula (1) is preferably 0.0000001 to 10% by mass with respect to the compound represented by the above general formula (2).

[0014] The content of the compound represented by the above general formula (2) is preferably 0.1 to 75% by mass with respect to the entire electrolyte, and the content of the compound represented by the above general formula (1) is preferably 0.001 to 5% by mass with respect to the compound represented by the above general formula (2).

[0015] The compound represented by the above general formula (1) is preferably CF2HCF2CH2ONa.

[0016] The compound represented by the above general formula (2) is preferably CF2HCF2CH2OCF2CF2H.

[0017] The present invention also relates to an electrochemical device including the above electrolyte.

[0018] The present invention also relates to a secondary battery including the above electrolyte.

[0019] The present invention also relates to a sodium secondary battery including the above electrolyte solution.

[0020] Advantages of the Invention The present invention can provide an electrolyte solution that can improve the durability of an electrochemical device, reduce the amount of gas generated, and reduce the amount of metal precipitation. In addition, the durability of an electrochemical device and a secondary battery using the electrolyte solution of the present invention is improved, and the amount of gas generated is reduced. Detailed Description of the Invention

[0021] Hereinafter, the present invention will be described in detail.

[0022] The electrolyte solution of the present invention contains at least one compound represented by the following general formula (1).

[0023] Rf 1 OR (1) (Rf 1 is a fluoroalkyl group having 1 to 5 carbon atoms. R is Na or K.) By including the specific alkali metal fluoroalkoxide in the electrolyte solution for an electrochemical device, the present invention can improve the durability (e.g., capacity retention rate after cycling) of the electrochemical device and can reduce the amount of gas generated during cycling of the electrochemical device and the amount of metal precipitation.

[0024] (Alkali metal fluoroalkoxide) The electrolyte solution of the present invention contains a compound represented by the following general formula (1).

[0025] Rf 1 OR (1) (Rf 1 is a fluoroalkyl group having 1 to 5 carbon atoms. R is Na or K.) From the viewpoint of protecting the positive electrode, Rf of the compound represented by the general formula (1) 1 is advantageous, and thus any one of the following formulas (1a) to (1e) is preferably used.

[0026] (1a) CF2HCF2 (1b) CF2HCF2CH2 (1c) CF3CHFCF2 (1d) CF3CF2CH2 (1e) CF2HCF2CF2CF2CH2 As the compound represented by the general formula (1), CF2HCF2CH2ONa is particularly preferably used from the viewpoints of cycling characteristics, suppression of gas generation amount, and suppression of metal precipitation amount.

[0027] The content of the compound represented by the above general formula (1) is preferably 0.01 to 10,000 ppm relative to the whole electrolyte. When having the content within this range, it is particularly excellent in terms of cycle characteristics, suppressing the amount of gas generation, and suppressing the amount of metal precipitation.

[0028] The lower limit of the content of the compound represented by the above general formula (1) is more preferably 0.1 ppm, further preferably 1 ppm, and particularly preferably 10 ppm. The upper limit of the content of the compound represented by the above general formula (1) is more preferably 1,000 ppm, and further preferably 100 ppm.

[0029] The compound represented by the above general formula (1) can be produced by a known method. For example, it can be obtained by reacting a fluoroalcohol (Rf 1 OH) with Na or K in the presence of a catalyst.

[0030] (fluoroether) The electrolyte of the present invention preferably further contains a compound represented by the following general formula (2) (hereinafter, sometimes referred to as fluoroether (2)).

[0031] Rf 2 ORf 3 (2) (Rf 2 、Rf 3 are independently fluoroalkyl groups having 1 to 8 carbon atoms.) By including fluoroether (2), the flame retardancy of the electrolyte is improved, and the stability and safety at high temperature and high voltage are improved. In addition, it is possible to further improve the durability of the electrochemical device, suppress the amount of gas generation during the cycle of the electrochemical device, and suppress the amount of metal precipitation.

[0032] The above fluoroalkyl group is a fluoroalkyl group having 1 to 8 carbon atoms. Among them, a fluoroalkyl group having 1 to 4 carbon atoms is preferred, and a fluoroalkyl group having 2 to 3 carbon atoms is more preferred.

[0033] If the number of carbon atoms of the fluoroalkyl group is too small, there is a tendency for the boiling point to become low. In addition, if the number of carbon atoms is too large, the solubility of the electrolyte salt decreases, and adverse effects on the compatibility with other solvents also start to occur. In addition, due to the increase in viscosity, there is a tendency for the rate performance to decrease. When the number of carbon atoms of Rf 2 is 3 or 4 and the number of carbon atoms of Rf 3 is 2 or 3, it is advantageous in terms of excellent boiling point and rate performance.

[0034] The fluorine content of fluoroether (2) is preferably 40 to 75% by mass. When having the fluorine content within this range, the balance between non-flammability and compatibility is particularly excellent. In addition, it is also preferred from the viewpoints of good oxidation resistance and safety.

[0035] The lower limit of the fluorine content is more preferably 45% by mass, further preferably 50% by mass, and particularly preferably 55% by mass. The upper limit is more preferably 70% by mass, and further preferably 66% by mass.

[0036] It should be noted that the fluorine content of the fluoroether (2) is a value calculated by {(the number of fluorine atoms × 19) / the molecular weight of the fluoroether (2)} × 100 (%) based on the structural formula of the fluoroether (2).

[0037] As Rf 2 , for example, the following can be cited: CF3CF2CH2-, CF3CFHCF2-, HCF2CF2CF2-, HCF2CF2CH2-, CF3CF2CH2CH2-, CF3CFHCF2CH2-, HCF2CF2CF2CF2-, HCF2CF2CF2CH2-, HCF2CF2CH2CH2-, HCF2CF(CF3)CH2-, etc.

[0038] In addition, as Rf 3 , for example, the following can be cited: -CH2CF2CF3, -CF2CFHCF3, -CF2CF2CF2H, -CH2CF2CF2H, -CH2CH2CF2CF3, -CH2CF2CFHCF3, -CF2CF2CF2CF2H, -CH2CF2CF2CF2H, -CH2CH2CF2CF2H, -CH2CF(CF3)CF2H, -CF2CF2H, -CH2CF2H, -CH2CF3, -CF2CH3, etc.

[0039] Specific examples of the above-mentioned fluoroether (2) include, for example: HCF2CF2CH2OCF2CF2H, CF3CF2CH2OCF2CF2H, HCF2CF2CH2OCF2CFHCF3, CF3CF2CH2OCF2CFHCF3, C6F 13 OCH3, C6F 13 OC2H5, C8F 17 OCH3, C8F 17 OC2H5, CF3CFHCF2CH(CH3)OCF2CFHCF3, HCF2CF2OCH(C2H5)2, HCF2CF2OC4H9, HCF2CF2OCH2CH(C2H5)2, HCF2CF2OCH2CH(CH3)2, etc.

[0040] As the above-mentioned fluoroether (2), particularly from the viewpoint of being advantageous in terms of flame retardancy, it is preferably at least one selected from CF2HCF2CH2OCF2CF2H, HCF2CF2CH2OCF2CFHCF3, and CF3CF2CH2OCF2CF2H.

[0041] Among them, CF2HCF2CH2OCF2CF2H is more preferred.

[0042] The content of the above-mentioned fluoroether (2) is preferably 0.1 to 90% by mass relative to the entire electrolyte. By setting it within this range, it can be used as a good electrolyte. That is, if the content increases, although the amount of metal precipitation from the active material decreases, the viscosity of the electrolyte becomes high, and in addition, the ionic conductivity decreases, so there is a tendency for the battery life to decrease.

[0043] The above lower limit is more preferably 0.5% by mass, and further preferably 1% by mass. The above upper limit is more preferably 80% by mass, further preferably 75% by mass, and particularly preferably 50% by mass.

[0044] The content of the compound represented by the above general formula (1) is preferably 0.0000001 to 10% by mass relative to the compound represented by the above general formula (2).

[0045] The above lower limit is more preferably 0.001% by mass, and further preferably 0.01% by mass. The above upper limit is more preferably 5% by mass, further preferably 1% by mass, and particularly preferably 0.5% by mass.

[0046] The electrolyte of the present invention preferably contains a solvent.

[0047] The above solvent preferably contains at least one selected from carbonates and carboxylates.

[0048] The above carbonate can be a cyclic carbonate or a chain carbonate.

[0049] The above cyclic carbonate can be an unfluorinated cyclic carbonate or a fluorinated cyclic carbonate.

[0050] As the above unfluorinated cyclic carbonate, an unfluorinated saturated cyclic carbonate can be cited, preferably an unfluorinated saturated alkylene carbonate having an alkylene group with 2 to 6 carbon atoms, and more preferably an unfluorinated saturated alkylene carbonate having an alkylene group with 2 to 4 carbon atoms.

[0051] Among them, as the above-mentioned unfluorinated saturated cyclic carbonate, from the viewpoints of high dielectric constant and appropriate viscosity, it is preferably at least one selected from ethylene carbonate, propylene carbonate, cis-2,3-pentylene carbonate, cis-2,3-butylene carbonate, 2,3-pentylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 1,2-butylene carbonate, and butylene carbonate.

[0052] The above-mentioned unfluorinated saturated cyclic carbonate can be used alone or in combination of two or more in any combination and ratio.

[0053] When the above-mentioned unfluorinated saturated cyclic carbonate is included, the content of the above-mentioned unfluorinated saturated cyclic carbonate is preferably 5 to 90% by volume, more preferably 10 to 60% by volume, and still more preferably 15 to 50% by volume with respect to the above-mentioned solvent.

[0054] The above-mentioned fluorinated cyclic carbonate is a cyclic carbonate having a fluorine atom. A solvent containing a fluorinated cyclic carbonate can be appropriately used even at a high voltage.

[0055] It should be noted that in this specification, "high voltage" means a voltage of 4.2 V or more. In addition, the upper limit of "high voltage" is preferably 4.9 V.

[0056] The above-mentioned fluorinated cyclic carbonate can be a fluorinated saturated cyclic carbonate or a fluorinated unsaturated cyclic carbonate.

[0057] The above-mentioned fluorinated saturated cyclic carbonate is a saturated cyclic carbonate having a fluorine atom. Specifically, compounds represented by the following general formula (A) can be cited: [Chemical formula 1]

[0058] (In the formula, X 1 ~X 4 are the same or different and each represents -H, -CH3, -C2H5, -F, a fluorinated alkyl group which may have an ether bond, or a fluorinated alkoxy group which may have an ether bond. Among them, at least one of X 1 ~X 4 is -F, a fluorinated alkyl group which may have an ether bond, or a fluorinated alkoxy group which may have an ether bond.). The above-mentioned fluorinated alkyl group means -CF3, -CF2H, -CH2F, etc.

[0059] If the above-mentioned fluorinated saturated cyclic carbonate is included, when the electrolyte of the present invention is applied to a high-voltage lithium ion secondary battery or the like, the antioxidant property of the electrolyte is improved, and stable and excellent charge-discharge characteristics can be obtained.

[0060] It should be noted that in this specification, "ether bond" is a bond represented by -O-.

[0061] From the viewpoints of good dielectric constant and oxidation resistance, one or two of X 1 ~X 4 are preferably -F, a fluoroalkyl group that may have an ether bond, or a fluoroalkoxy group that may have an ether bond.

[0062] From the viewpoints of expecting a decrease in viscosity at low temperatures, an increase in flash point, and an improvement in the solubility of electrolyte salts, X 1 ~X 4 is preferably -H, -F, a fluoroalkyl group (a), a fluoroalkyl group having an ether bond (b), or a fluoroalkoxy group (c).

[0063] The above-mentioned fluoroalkyl group (a) is a group obtained by substituting at least one of the hydrogen atoms of the alkyl group with a fluorine atom. The number of carbon atoms of the fluoroalkyl group (a) is preferably 1 to 20, more preferably 1 to 17, still more preferably 1 to 7, and particularly preferably 1 to 5.

[0064] If the number of carbon atoms is too large, the low-temperature characteristics may decrease or the solubility of the electrolyte salt may decrease; if the number of carbon atoms is too small, a decrease in the solubility of the electrolyte salt, a decrease in discharge efficiency, and an increase in viscosity may sometimes be observed.

[0065] In the above-mentioned fluoroalkyl group (a), as the fluoroalkyl group having 1 carbon atom, CFH2-, CF2H-, and CF3- can be mentioned. In particular, CF2H- or CF3- is preferred in terms of high-temperature storage characteristics, and CF3- is most preferred.

[0066] The fluorine content of the fluoroalkyl group (a), the fluoroalkyl group having an ether bond (b), and the fluoroalkoxy group (c) in the above-mentioned fluorinated saturated cyclic carbonate is preferably 10% by mass or more. If the fluorine content is too low, it may not be possible to sufficiently obtain the effects of reducing viscosity at low temperatures and increasing the flash point. From the above viewpoints, the fluorine content is more preferably 12% by mass or more, and still more preferably 15% by mass or more. The upper limit is usually 76% by mass.

[0067] The fluorine content of the fluoroalkyl group (a), the fluoroalkyl group having an ether bond (b), and the fluoroalkoxy group (c) is a value calculated by {(the number of fluorine atoms × 19) / the formula weight of each group} × 100 (%) based on the structural formula of each group.

[0068] In addition, from the viewpoints of good dielectric constant and oxidation resistance, the fluorine content of the entire above-mentioned fluorinated saturated cyclic carbonate is preferably 10% by mass or more, and more preferably 15% by mass or more. The upper limit is usually 76% by mass.

[0069] It should be noted that the fluorine content of the above fluorinated saturated cyclic carbonates is a value calculated by { (the number of fluorine atoms × 19) / the molecular weight of the fluorinated saturated cyclic carbonate} × 100 (%) based on the structural formula of the fluorinated saturated cyclic carbonate.

[0070] As the above fluorinated saturated cyclic carbonates, specifically, for example, the following can be cited.

[0071] As X 1 ~X 4 Specific examples of the fluorinated saturated cyclic carbonates in which at least one of them is -F can include: [Chemical formula 2]

[0072] etc. These compounds have high breakdown voltage and good solubility of electrolyte salts.

[0073] Among them, as the above fluorinated saturated cyclic carbonates, any one of the following compounds is preferred.

[0074] [Chemical formula 3]

[0075] [Chemical formula 4]

[0076] As the above fluorinated saturated cyclic carbonates, among them, fluoroethylene carbonate, difluoroethylene carbonate, ethyl trifluoromethyl carbonate (3,3,3-trifluoropropylene carbonate), and ethyl 2,2,3,3,3-pentafluoropropyl carbonate are more preferred.

[0077] The above fluorinated cyclic carbonates can be used alone or in combination of two or more in any combination and ratio.

[0078] When the above fluorinated cyclic carbonates are included, the content of the above fluorinated cyclic carbonates is preferably 5 to 90% by volume, more preferably 10 to 60% by volume, and further preferably 15 to 45% by volume with respect to the above solvent.

[0079] The above linear carbonates can be non-fluorinated linear carbonates or fluorinated linear carbonates.

[0080] As the above-mentioned non-fluorinated chain carbonates, examples thereof include: CH3OCOOCH3 (dimethyl carbonate: DMC), CH3CH2OCOOCH2CH3 (diethyl carbonate: DEC), CH3CH2OCOOCH3 (ethyl methyl carbonate: EMC), CH3OCOOCH2CH2CH3 (methyl propyl carbonate), methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, dibutyl carbonate, methyl isopropyl carbonate, methyl-2-phenylphenyl carbonate, phenyl-2-phenylphenyl carbonate, trans-2,3-pentylene carbonate, trans-2,3-butylene carbonate, ethyl phenyl carbonate and other hydrocarbon-based chain carbonates. Among them, at least one selected from ethyl methyl carbonate, diethyl carbonate and dimethyl carbonate is preferred.

[0081] The above-mentioned non-fluorinated chain carbonates can be used alone or in combination of two or more in any combination and ratio.

[0082] When the above-mentioned non-fluorinated chain carbonates are included, the content of the above-mentioned non-fluorinated chain carbonates is preferably 10 to 90% by volume, more preferably 20 to 85% by volume, and further preferably 30 to 80% by volume with respect to the above-mentioned solvent.

[0083] The above-mentioned carboxylic acid ester can be a cyclic carboxylic acid ester or a chain carboxylic acid ester.

[0084] The above-mentioned cyclic carboxylic acid ester can be a non-fluorinated cyclic carboxylic acid ester or a fluorinated cyclic carboxylic acid ester.

[0085] As the above-mentioned non-fluorinated cyclic carboxylic acid ester, non-fluorinated saturated cyclic carboxylic acid esters are exemplified, and non-fluorinated saturated cyclic carboxylic acid esters having an alkylene group with 2 to 4 carbon atoms are preferred.

[0086] Specific examples of the non-fluorinated saturated cyclic carboxylic acid ester having an alkylene group with 2 to 4 carbon atoms include β -propiolactone, γ -butyrolactone, ε -caprolactone, δ -valerolactone, α methyl- γ -butyrolactone. Among them, from the viewpoints of improving lithium ion dissociation degree and improving loading characteristics, γ -butyrolactone, δ -valerolactone are particularly preferred.

[0087] The above-mentioned non-fluorinated saturated cyclic carboxylic acid esters can be used alone or in combination of two or more in any combination and ratio.

[0088] In the case of containing the above-mentioned unfluorinated saturated cyclic carboxylic acid ester, the content of the above-mentioned unfluorinated saturated cyclic carboxylic acid ester relative to the above-mentioned solvent is preferably 0 to 90% by volume, more preferably 0.001 to 90% by volume, still more preferably 1 to 60% by volume, and particularly preferably 5 to 40% by volume.

[0089] The above-mentioned chain carboxylic acid ester may be an unfluorinated chain carboxylic acid ester or a fluorinated chain carboxylic acid ester. In the case where the above-mentioned solvent contains the above-mentioned chain carboxylic acid ester, an increase in the resistance of the electrolytic solution after high-temperature storage can be further suppressed.

[0090] The above-mentioned solvent preferably contains at least one selected from the above-mentioned cyclic carbonates, the above-mentioned chain carbonates, and the above-mentioned chain carboxylic acid esters. The above-mentioned cyclic carbonate is preferably a saturated cyclic carbonate.

[0091] The electrolytic solution containing the solvent having the above composition can further improve the high-temperature storage characteristics and cycling characteristics of the electrochemical device.

[0092] In the case where the above-mentioned solvent contains the above-mentioned cyclic carbonate and at least one selected from the above-mentioned chain carbonates and the above-mentioned chain carboxylic acid esters, the above-mentioned cyclic carbonate and at least one selected from the above-mentioned chain carbonates and the above-mentioned chain carboxylic acid esters preferably contain 10 to 100% by volume in total, more preferably 30 to 100% by volume, and still more preferably 50 to 100% by volume.

[0093] In the case where the above-mentioned solvent contains the above-mentioned cyclic carbonate and at least one selected from the above-mentioned chain carbonates and the above-mentioned chain carboxylic acid esters, the volume ratio of the above-mentioned cyclic carbonate to at least one selected from the above-mentioned chain carbonates and the above-mentioned chain carboxylic acid esters is preferably 5 / 95 to 95 / 5; more preferably 10 / 90 or more, still more preferably 15 / 85 or more, and particularly preferably 20 / 80 or more; more preferably 90 / 10 or less, still more preferably 60 / 40 or less, and particularly preferably 50 / 50 or less.

[0094] The above-mentioned solvent also preferably contains at least one selected from the above-mentioned unfluorinated saturated cyclic carbonates, the above-mentioned unfluorinated chain carbonates, and the above-mentioned unfluorinated chain carboxylic acid esters. The electrolytic solution containing the solvent having the above composition can be suitably used for an electrochemical device used at a lower voltage.

[0095] In the case where the above-mentioned solvent contains the above-mentioned unfluorinated saturated cyclic carbonate and at least one selected from the above-mentioned unfluorinated chain carbonates and the above-mentioned unfluorinated chain carboxylic acid esters, the above-mentioned unfluorinated saturated cyclic carbonate and at least one selected from the above-mentioned unfluorinated chain carbonates and the above-mentioned unfluorinated chain carboxylic acid esters preferably contain 5 to 100% by volume in total, more preferably 20 to 100% by volume, and still more preferably 30 to 100% by volume.

[0096] When the above electrolyte contains the above non-fluorinated saturated cyclic carbonate and at least one selected from the above non-fluorinated linear carbonate and the above non-fluorinated linear carboxylate, the volume ratio of the above non-fluorinated saturated cyclic carbonate to at least one selected from the above non-fluorinated linear carbonate and the above non-fluorinated linear carboxylate is preferably 5 / 95 to 95 / 5; more preferably 10 / 90 or more, further preferably 15 / 85 or more, particularly preferably 20 / 80 or more; more preferably 90 / 10 or less, further preferably 60 / 40 or less, particularly preferably 50 / 50 or less.

[0097] The above solvent preferably further contains at least one selected from the above fluorinated saturated cyclic carbonate, the above fluorinated linear carbonate, and the above fluorinated linear carboxylate. The electrolyte containing the solvent having the above composition can be suitably used not only for electrochemical devices used at lower voltages but also for electrochemical devices used at higher voltages.

[0098] The above solvent is preferably a non-aqueous solvent, and the electrolyte of the present invention is preferably a non-aqueous electrolyte.

[0099] The content of the above solvent in the electrolyte is preferably 70 to 99.999% by mass, more preferably 80% by mass or more, and more preferably 92% by mass or less.

[0100] The electrolyte of the present invention preferably further contains an electrolyte salt (wherein, the above compound (5) is not included). As the above electrolyte salt, in addition to alkali metal salts, ammonium salts, other metal salts other than alkali metal salts (for example, light metal salts other than alkali metal salts), liquid salts (ionic liquids), inorganic polymer salts, organic polymer salts, etc., any salts that can be used in electrolytes can be used.

[0101] As the electrolyte salt for the electrolyte of the electrochemical device, for example, the following compounds can be cited. MPF6, MBF4, MClO4, MAsF6, MB(C6H5)4, MCH3SO3, MCF3SO3, MAlCl4, M2SiF6, MCl, MBr. (In the formula, M is at least one metal selected from Li, Na, and K, preferably one metal selected from Li, Na, and K, more preferably Li or Na.) By using these alkali metal salts, excellent battery capacity, cycle characteristics, storage characteristics, etc. can be obtained. Among them, at least one selected from MPF6, MBF4, MClO4, and MAsF6 is preferred, and MPF6 is more preferred. By using these alkali metal salts, the internal resistance can be further reduced, and higher effects can be obtained.

[0102] As the electrolyte salt for the sodium ion secondary battery electrolyte, a sodium salt is preferred.

[0103] As the above-mentioned sodium salt, any sodium salt can be used. Specifically, the following sodium salts can be mentioned. For example, NaPF6, NaBF4, NaClO4, NaAlF4, NaSbF6, NaTaF6, NaWF7, NaAsF6, NaAlCl4, NaI, NaBr, NaCl, NaB 10 Cl 10 , inorganic sodium salts such as Na2SiF6, Na2PFO3, NaPO2F2; Sodium tungstates such as NaWOF5; Carboxylate sodium salts such as HCO2Na, CH3CO2Na, CH2FCO2Na, CHF2CO2Na, CF3CO2Na, CF3CH2CO2Na, CF3CF2CO2Na, CF3CF2CF2CO2Na, CF3CF2CF2CF2CO2Na; Sodium salts having an S=O group such as FSO3Na, CH3SO3Na, CH2FSO3Na, CHF2SO3Na, CF3SO3Na, CF3CF2SO3Na, CF3CF2CF2SO3Na, CF3CF2CF2CF2SO3Na, sodium methyl sulfate, sodium ethyl sulfate (C2H5OSO3Na), sodium 2,2,2-trifluoroethyl sulfate; Imide sodium salts such as NaN(FCO)2, NaN(FCO)(FSO2), NaN(FSO2)2, NaN(FSO2)(CF3SO2), NaN(CF3SO2)2, NaN(C2F5SO2)2, sodium bis(perfluoroethanesulfonyl)imide, cyclic 1,2-perfluorobutane disulfonylimide sodium salt, cyclic 1,3-perfluoropropane disulfonylimide sodium salt, cyclic 1,2-ethane disulfonylimide sodium salt, cyclic 1,3-propane disulfonylimide sodium salt, cyclic 1,4-perfluorobutane disulfonylimide sodium salt, NaN(CF3SO2)(FSO2), NaN(CF3SO2)(C3F7SO2), NaN(CF3SO2)(C4F9SO2), NaN(POF2)2; Methylated sodium salts such as NaC(FSO2)3, NaC(CF3SO2)3, NaC(C2F5SO2)3; and NaPF a (C n F 2n＋1 ) 6-aSalts represented by the formula (wherein a is an integer from 0 to 5 and n is an integer from 1 to 6), such as NaPF3(C2F5)3, NaPF3(CF3)3, NaPF3(iso-C3F7)3, NaPF5(iso-C3F7), NaPF4(CF3)2, NaPF4(C2F5)2, NaPF4(CF3SO2)2, NaPF4(C2F5SO2)2, NaBF3CF3, NaBF3C2F5, NaBF3C3F7, NaBF2(CF3)2, NaBF2(C2F5)2, NaBF2(CF3SO2)2, NaBF2(C2F5SO2)2 and other fluorinated organic sodium salts, NaSCN, LiB(CN)4, NaB(CN)4, NaB(C6H5)4, Na2(C2O4), NaP(C2O4)3, Na2B 12 F b H 12-b and so on (where b is an integer from 0 to 3).

[0104] Among them, from the viewpoint of having effects such as improving output characteristics, high-rate charge and discharge characteristics, high-temperature storage characteristics, and cycle characteristics, NaPF6, NaBF4, NaSbF6, NaTaF6, NaPO2F2, FSO3Na, CF3SO3Na, NaN(FSO2)2, NaN(FSO2)(CF3SO2), NaN(CF3SO2)2, NaN(C2F5SO2)2, cyclic 1,2-perfluoroethane disulfonimide sodium, cyclic 1,3-perfluoropropane disulfonimide sodium, NaC(FSO2)3, NaC(CF3SO2)3, NaC(C2F5SO2)3, NaBF3CF3, NaBF3C2F5, NaPF3(CF3)3, NaPF3(C2F5)3, etc. are particularly preferred, and the most preferred is at least one sodium salt selected from NaPF6, NaN(FSO2)2 and NaBF4.

[0105] As the electrolyte salt of the electrolyte for the lithium ion secondary battery, a lithium salt is preferred.

[0106] As the above lithium salt, any lithium salt can be used. Specifically, the following lithium salts can be cited. For example, LiPF6, LiBF4, LiClO4, LiAlF4, LiSbF6, LiTaF6, LiWF7, LiAsF6, LiAlCl4, LiI, LiBr, LiCl, LiB 10 Cl 10 and inorganic lithium salts such as Li2SiF6, Li2PFO3, LiPO2F2; Lithium tungstates such as LiWOF5; Lithium carboxylates such as HCO2Li, CH3CO2Li, CH2FCO2Li, CHF2CO2Li, CF3CO2Li, CF3CH2CO2Li, CF3CF2CO2Li, CF3CF2CF2CO2Li, CF3CF2CF2CF2CO2Li, etc.; Lithium salts with S=O groups such as FSO3Li, CH3SO3Li, CH2FSO3Li, CHF2SO3Li, CF3SO3Li, CF3CF2SO3Li, CF3CF2CF2SO3Li, CF3CF2CF2CF2SO3Li, lithium methyl sulfate, lithium ethyl sulfate (C2H5OSO3Li), lithium 2,2,2-trifluoroethyl sulfate, etc.; Lithium imide salts such as LiN(FCO)2, LiN(FCO)(FSO2), LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium bis(perfluoroethanesulfonyl)imide, cyclic lithium 1,2-perfluoroethanedisulfonylimide, cyclic lithium 1,3-perfluoropropanedisulfonylimide, cyclic lithium 1,2-ethanedisulfonylimide, cyclic lithium 1,3-propanedisulfonylimide, cyclic lithium 1,4-perfluorobutane disulfonylimide, LiN(CF3SO2)(FSO2), LiN(CF3SO2)(C3F7SO2), LiN(CF3SO2)(C4F9SO2), LiN(POF2)2, etc.; Lithium amidosulfate compounds such as (CF3CH2)2NSO3Li, (CF3CH2)(CH3)NSO3Li, (CNCH2)2NSO3Li, etc.; Methylated lithium salts such as LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, etc.; and LiPF a (C n F 2n＋1 ) 6-a(wherein a is an integer of 0 to 5 and n is an integer of 1 to 6) salts (e.g., LiPF3(C2F5)3, LiPF3(CF3)3, LiPF3(iso-C3F7)3, LiPF5(iso-C3F7), LiPF4(CF3)2, LiPF4(C2F5)2, LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF3CF3, LiBF3C2F5, LiBF3C3F7, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2 and other fluorinated organic lithium salts, LiSCN, LiB(CN)4, LiB(C6H5)4, Li2(C2O4), LiP(C2O4)3, Li2B 12 F b H 12-b (where b is an integer of 0 to 3), etc.

[0107] Among them, from the viewpoint of having effects such as improving output characteristics, high-rate charge-discharge characteristics, high-temperature storage characteristics, and cycle characteristics, LiPF6, LiBF4, LiSbF6, LiTaF6, LiPO2F2, FSO3Li, CF3SO3Li, LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic lithium 1,2-perfluoroethanedisulfonimide, cyclic lithium 1,3-perfluoropropanedisulfonimide, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, LiPF3(C2F5)3, etc. are particularly preferred, and lithium salts selected from at least one of LiPF6, LiN(FSO2)2 and LiBF4 are most preferred.

[0108] These electrolyte salts can be used alone or in combination of two or more. In the case of using two or more in combination, preferred examples are the combination of LiPF6 and LiBF4, the combination of LiPF6 and LiPO2F2, C2H5OSO3Li or FSO3Li, which have the effect of improving high-temperature storage characteristics, load characteristics, and cycle characteristics.

[0109] In this case, the blending amount of LiBF4, LiPO2F2, C2H5OSO3Li, or FSO3Li relative to 100% by mass of the entire electrolyte solution is not limited and may be arbitrary as long as the effects of the present invention are not significantly impaired. Relative to the electrolyte solution of the present invention, it is usually 0.01% by mass or more, preferably 0.1% by mass or more. In addition, it is usually 30% by mass or less, preferably 20% by mass or less, more preferably 10% by mass or less, and further preferably 5% by mass or less.

[0110] In addition, another example is the combined use of an inorganic lithium salt and an organic lithium salt, and the combined use of these two has the effect of suppressing deterioration caused by high-temperature storage. As the organic lithium salt, CF3SO3Li, LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic lithium 1,2-perfluoroethanedisulfonimide, cyclic lithium 1,3-perfluoropropanedisulfonimide, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, LiPF3(C2F5)3, etc. are preferred. In this case, the proportion of the organic lithium salt relative to 100% by mass of the entire electrolyte solution is preferably 0.1% by mass or more, particularly preferably 0.5% by mass or more; and it is preferably 30% by mass or less, particularly preferably 20% by mass or less.

[0111] The concentration of these electrolyte salts in the electrolyte solution is not particularly limited as long as the effects of the present invention are not impaired. From the viewpoint of making the conductivity of the electrolyte solution within a good range and ensuring good battery performance, the total molar concentration of lithium in the electrolyte solution is preferably 0.3 mol / L or more, more preferably 0.4 mol / L or more, and further preferably 0.5 mol / L or more; and it is preferably 3 mol / L or less, more preferably 2.5 mol / L or less, and further preferably 2.0 mol / L or less.

[0112] If the total molar concentration of lithium is too low, there may be a case where the conductivity of the electrolyte solution is insufficient; on the other hand, if the concentration is too high, there may be a case where the conductivity decreases due to an increase in viscosity, and the battery performance may decrease.

[0113] The electrolyte solution of the present invention may further contain a fluorinated saturated cyclic carbonate, an unsaturated cyclic carbonate, an overcharge prevention agent, other known additives, etc. as additives. Thereby, a decrease in the characteristics of the electrochemical device can be suppressed.

[0114] The electrolyte of the present invention may further contain, within the range not impairing the effects of the present invention, ether compounds other than the fluoroethers represented by the above general formula (2), cyclic and chain carboxylic acid esters, nitrogen-containing compounds, boron-containing compounds, organosilicon-containing compounds, nonflammable (flame retardant) agents, surfactants, high dielectric constant additives, cycle property and rate property improvers, sulfone compounds, etc. as additives.

[0115] As the above ether compounds, linear ethers having 2 to 10 carbon atoms and cyclic ethers having 3 to 6 carbon atoms are preferred.

[0116] Examples of the linear ethers having 2 to 10 carbon atoms include: dimethyl ether, diethyl ether, di-n-butyl ether, dimethoxymethane, methoxyethoxymethane, diethoxymethane, dimethoxyethane, methoxyethoxyethane, diethoxyethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol, diethylene glycol dimethyl ether, pentaethylene glycol, triethylene glycol dimethyl ether, triethylene glycol, tetraethylene glycol, tetraethylene glycol dimethyl ether, diisopropyl ether, etc.

[0117] Examples of the cyclic ethers having 3 to 6 carbon atoms include: 1,2-dioxane, 1,3-dioxane, 2-methyl-1,3-dioxane, 4-methyl-1,3-dioxane, 1,4-dioxane, trioxane, 2-methyl-1,3-dioxolane, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 2-(trifluoroethyl)dioxolane, 2,2,-bis(trifluoromethyl)-1,3-dioxolane, etc., and their fluorinated compounds. Among them, in terms of high solvation ability for lithium ions and improvement of ion dissociation degree, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether, and crown ether are preferred; from the viewpoints of low viscosity and provision of high ionic conductivity, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are particularly preferred.

[0118] The content of hydrogen fluoride (HF) in the electrolyte of the present invention is preferably 5 to 200 ppm. By containing HF, the formation of the coating film of the above additives can be promoted. If the content of HF is too small, the ability to form a coating film on the negative electrode is reduced, and there is a tendency for the characteristics of the electrochemical device to deteriorate. In addition, if the content of HF is too large, there is a tendency for the oxidation resistance of the electrolyte to deteriorate due to the influence of HF. Even if the electrolyte of the present invention contains HF within the above range, the high-temperature storage property and capacity recovery rate of the electrochemical device will not be reduced.

[0119] The content of HF is more preferably 10 ppm or more, and further preferably 20 ppm or more. In addition, the content of HF is more preferably 100 ppm or less, further preferably 80 ppm or less, and particularly preferably 50 ppm or less.

[0120] The content of HF can be determined by neutralization titration.

[0121] The electrolyte of the present invention can be prepared by any method using the above components.

[0122] The electrolyte of the present invention can be suitably used for electrochemical devices such as sodium ion secondary batteries, lithium ion secondary batteries, lithium ion capacitors, hybrid capacitors, electric double layer capacitors, etc. An electrochemical device having the electrolyte of the present invention is also one of the present inventions.

[0123] (Electrochemical device) As the above-mentioned electrochemical device, there is no particular limitation, and it can be applied to conventionally well-known electrochemical devices. Specifically, examples include: secondary batteries such as sodium ion batteries and lithium ion batteries, primary batteries such as lithium batteries, magnesium ion batteries, radical batteries, solar cells (especially dye-sensitized solar cells), fuel cells; capacitors such as lithium ion capacitors, hybrid capacitors, electrochemical capacitors, and electric double layer capacitors; Various capacitors such as aluminum electrolytic capacitors and tantalum electrolytic capacitors; Electrochromic elements, electrochemical switch elements, various electrochemical sensors, etc.

[0124] Among them, due to its high capacity and large output, it can also be suitably used for secondary batteries with large volume changes caused by the movement of a large amount of metal ions.

[0125] The above-mentioned secondary battery can adopt a well-known structure. Typically, it includes a positive electrode and a negative electrode capable of absorbing and releasing ions (such as lithium ions, sodium ions, etc.), and the electrolyte of the present invention. A secondary battery having the electrolyte of the present invention is also one of the present inventions.

[0126] Hereinafter, a secondary battery having the electrolyte of the present invention will be described.

[0127] The present invention also relates to a lithium ion secondary battery or a sodium ion secondary battery having the electrolyte of the present invention. The above-mentioned secondary battery preferably includes a positive electrode, a negative electrode, and the above-mentioned electrolyte. A sodium ion secondary battery having the electrolyte of the present invention is also one of the present inventions.

[0128] <Positive electrode> The positive electrode preferably consists of a positive electrode active material layer containing a positive electrode active material and a current collector.

[0129] As the above-mentioned positive electrode active material, there is no particular limitation as long as it can electrochemically absorb and release alkali metal ions. For example, a material containing an alkali metal and at least one transition metal is preferably used. As a specific example, a transition metal composite oxide containing an alkali metal and a transition metal phosphate compound containing an alkali metal can be cited. Among them, as the positive electrode active material, a transition metal composite oxide containing an alkali metal capable of generating a high voltage is particularly preferred. As the above-mentioned alkali metal ions, lithium ions, sodium ions, potassium ions, etc. can be cited. In a preferred embodiment, the alkali metal ion can be a lithium ion or a sodium ion. That is, in this embodiment, the alkali metal ion secondary battery is a lithium ion secondary battery or a sodium ion secondary battery.

[0130] As the above-mentioned transition metal composite oxide containing an alkali metal, for example, Formula (3-1): MaMn 2-b M 1 b O4 (In the formula, M is at least one metal selected from Li, Na, and K; 0.9 ≤ a; 0 ≤ b ≤ 1.5; M 1 is at least one metal selected from Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge) The lithium-manganese spinel composite oxide shown; Formula (3-2): MNi 1-c M 2 c O2 (In the formula, M is at least one metal selected from Li, Na, and K; 0 ≤ c ≤ 0.5; M 2 is at least one metal selected from Fe, Co, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge) The lithium-nickel composite oxide shown; or Formula (3-3): MCo 1-d M 3 d O2 (In the formula, M is at least one metal selected from Li, Na, and K; 0 ≤ d ≤ 0.5; M 3 is at least one metal selected from Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge) The lithium-cobalt composite oxide shown. Among the above, M is preferably one metal selected from Li, Na, and K, and more preferably Li or Na.

[0131] Among them, from the perspective of providing a secondary battery with high energy density and high output, MCoO2, MMnO2, MNiO2, MMn2O4, MNi 0.8 Co 0.15 Al 0.05 O2, or MNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc. are preferred, and the compound represented by the following formula (3-4) is preferred.

[0132] MNi h Co i Mn j M 5 k O2 (3-4) (In the formula, M is at least one metal selected from Li, Na, and K, and M 5 represents at least one selected from Fe, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge, (h + i + j + k) = 1.0, 0 ≤ h ≤ 1.0, 0 ≤ i ≤ 1.0, 0 ≤ j ≤ 1.5, 0 ≤ k ≤ 0.2.) As the material of the current collector for the positive electrode, metal materials such as aluminum, titanium, tantalum, stainless steel, nickel, or their alloys can be mentioned; carbon materials such as carbon cloth and carbon paper. Among them, metal materials are preferred, and aluminum or its alloy is particularly preferred.

[0133] The positive electrode can be manufactured according to a conventional method. For example, a positive electrode mixture in a slurry form can be prepared by adding a binder, a thickener, a conductive material, a solvent, etc. to the above positive electrode active material, and it is coated on the current collector and pressed after drying to achieve high density.

[0134] The above high density can be achieved by manual pressing, roll pressing, etc. The density of the positive electrode active material layer is preferably 1.5 g / cm 3 or more, more preferably 2 g / cm 3 or more, further preferably 2.2 g / cm 3 or more, and preferably 5 g / cm 3 or less, more preferably 4.5 g / cm 3 or less, further preferably 4 g / cm 3 or less. If it exceeds this range, the permeability of the electrolyte to the vicinity of the current collector / active material interface decreases, and in particular, the charge-discharge characteristics at high current density decrease, and sometimes high output cannot be obtained. In addition, if it is lower than this range, the conductivity between the active materials decreases, the battery resistance increases, and sometimes high output cannot be obtained.

[0135] <Negative electrode> The negative electrode preferably consists of a negative electrode active material layer and a current collector.

[0136] (Negative electrode active material) As the negative electrode active material, there is no particular limitation, and examples thereof include: any one selected from lithium metal, substances containing carbonaceous materials such as artificial graphite, graphite carbon fiber, hard carbon, resin-fired carbon, thermally decomposed vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl resin-fired carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, and hardly graphitizable carbon, silicon and silicon compounds such as silicon alloys, Li4Ti5O 12 and the like, or a mixture of two or more thereof. Among them, substances containing carbonaceous materials and silicon compounds can be particularly preferably used at least in part.

[0137] As the current collector included in the negative electrode of the present invention, examples include metal foils or metal meshes such as iron, stainless steel, copper, aluminum, nickel, and titanium, carbon materials such as carbon cloth and carbon paper, and among them, copper foil is preferred.

[0138] The negative electrode can be appropriately manufactured by a manufacturing method of coating the above-mentioned negative electrode mixture on the current collector. After coating the negative electrode mixture, the coating film can be further dried, heat-treated arbitrarily, and the obtained dried coating film can be pressed.

[0139] As the shape of the current collector, in the case of a metal material, examples include metal foil, metal cylinder, metal coil, metal plate, expanded metal, stamped metal, foamed metal, etc., and in the case of a carbon material, examples include carbon plate, carbon film, carbon cylinder, etc. Among them, metal foil is preferred. It should be noted that the film can be appropriately formed into a mesh shape. The thickness of the film is arbitrary, usually 1 μ m or more, preferably 3 μ m or more, more preferably 5 μ m or more; and usually 1 mm or less, preferably 100 μ m or less, more preferably 50 μ m or less. If the film is thinner than this range, the strength required as a current collector may sometimes be insufficient. On the contrary, if the film is thicker than this range, the processability may sometimes be impaired.

[0140] <Separator> The secondary battery of the present invention preferably further has a separator.

[0141] The material and shape of the above-mentioned separator are not particularly limited as long as they are stable in the electrolyte and have excellent liquid retention properties, and known materials or shapes can be used. Among them, porous sheets or non-woven fabric-like articles formed of materials stable to the electrolyte of the present invention, such as resins, glass fibers, and inorganic substances, and having excellent liquid retention properties are preferred.

[0142] As materials for resin and glass fiber separators, for example, polyolefins such as polyethylene and polypropylene, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, glass filters, etc. can be used. Polypropylene / polyethylene double-layer films, polypropylene / polyethylene / polypropylene three-layer films, etc. These materials can be used alone or two or more kinds can be used in any combination and ratio. Among them, in terms of good electrolyte permeability or shut-off effect, the above-mentioned separator is preferably a porous sheet or non-woven fabric made of polyolefins such as polyethylene and polypropylene as raw materials.

[0143] The thickness of the separator is arbitrary, usually 1 μ μm or more, preferably 5 μ μm or more, more preferably 8 μ μm or more; and, usually 50 μ μm or less, preferably 40 μ μm or less, more preferably 30 μ μm or less. If the separator is too thin compared to the above range, the insulation or mechanical strength may sometimes decrease. In addition, if it is too thick compared to the above range, not only may the battery performance such as rate characteristics decrease, but also the energy density of the entire electrolyte battery may sometimes decrease.

[0144] <Battery Design> The electrode group can be either an electrode group with a laminated structure formed by separating the above-mentioned positive electrode plate and negative electrode plate with the above-mentioned separator, or an electrode group with a structure formed by winding the above-mentioned positive electrode plate and negative electrode plate in a spiral shape with the above-mentioned separator in between. The proportion of the volume of the electrode group in the internal volume of the battery (hereinafter, referred to as the electrode group occupancy rate) is usually 40% or more, preferably 50% or more; and, usually 90% or less, preferably 80% or less.

[0145] The material of the outer casing is not particularly limited as long as it is a substance stable with respect to the electrolyte used. Specifically, metals such as nickel-plated steel sheets, stainless steel, aluminum or aluminum alloys, magnesium alloys, etc. can be used, or a laminated film (laminate film) of resin and aluminum foil. From the viewpoint of weight reduction, it is preferable to use metals such as aluminum or aluminum alloys, and laminate films.

[0146] The shape of the secondary battery of the present invention is arbitrary, and examples thereof include cylindrical, square, laminated, coin-shaped, large-sized, etc. It should be noted that the shapes and configurations of the positive electrode, negative electrode, and separator can be changed according to the shape of each battery.

[0147] Examples Hereinafter, examples are given to illustrate the present invention, but the present invention is not limited to the above examples.

[0148] In the following examples, unless otherwise specified, "parts" and "%" represent "parts by weight" and "wt%", respectively.

[0149] The compounds (1-1) to (1-10) to be used are shown below.

[0150] (1-1) CF2HCF2CH2ONa (1-2) CF2HCF2CH2OK (1-3) CF2HCF2CF2CF2CH2ONa (1-4) CF2HCF2CF2CF2CH2OK (1-5) CF2HCF2ONa (1-6) CF2HCF2OK (1-7) CF3CHFCF2ONa (1-8) CF3CHFCF2OK (1-9) CF3CF2CH2ONa (1-10) CF3CF2CH2OK The compounds (2-1) to (2-3) to be used are shown below.

[0151] (2-1) CF2HCF2CH2OCF2CF2H (2-2) CF2HCF2CH2OCF2CHFCF3 (2-3) CF3CF2CH2OCF2CF2H (Example 1) [Preparation of electrolyte solution] Ethylene carbonate (EC), diethyl carbonate (DEC), and fluoroethylene carbonate (FEC) were mixed at a volume ratio of 30 / 68 / 2, and NaPF6 was added to the mixture at a concentration of 1.0 mol / L to prepare a basic electrolyte solution.

[0152] 0.1 ppm of compound (1-1) was added to the above basic electrolyte solution and mixed to prepare a non-aqueous electrolyte solution.

[0153] [Fabrication of positive electrode] 97 parts by weight of NaCoO2 as a positive electrode active material, 1.5 parts by weight of acetylene black as a conductive assistant, and 1.5 parts by weight of polyvinylidene fluoride (8 wt% NMP solution) as a binder were added, and the mixture was mixed using a disperser and made into a slurry. The resulting slurry was coated on a 20-μm-thick μAluminum foil of m is dried, and after rolling with a rolling press, it is cut into a shape with a coated part (positive electrode material layer) having a width of 50 mm and a length of 30 mm and an uncoated part having a width of 5 mm and a length of 9 mm to produce a positive electrode.

[0154] [Fabrication of Negative Electrode] 94% by mass of hard carbon as the negative electrode active material and 6% by mass of polyvinylidene fluoride (PVdF) as the binder are mixed, and then N-methyl-2-pyrrolidone (NMP) is added for mixing to form a slurry. The obtained slurry is coated on a negative electrode current collector including a copper foil with a thickness of 15 μ m, and it is dried. It is cut into a specified electrode size and rolled with a roll press, thereby fabricating a negative electrode having a negative electrode material layer formed on the negative electrode current collector.

[0155] [Fabrication of Battery] The fabricated negative electrode having a negative electrode material layer on one side is cut into a shape with a coated part (negative electrode material layer) having a width of 52 mm and a length of 32 mm and an uncoated part having a width of 5 mm and a length of 9 mm to produce a negative electrode.

[0156] The above positive electrode and negative electrode are opposed to each other with a microporous polyethylene film (separator) having a thickness of 20 μ m, and the non-aqueous electrolyte obtained above is injected. After the non-aqueous electrolyte sufficiently penetrates into the separator and the like, it is sealed and pre-charged and aged to fabricate an aluminum laminated battery (sodium ion secondary battery).

[0157] (Measurement of Battery Characteristics) [Cycle Characteristics] The obtained aluminum laminated battery is charged at a constant current-constant voltage (hereinafter referred to as CC / CV charging) at a current equivalent to 0.2C at 25 °C (0.1C cut-off) to 3.8V, and then discharged at a constant current of 0.2C to 1.5V. This is taken as 1 cycle, and 3 cycles are implemented. Then, at 45 °C, it is charged at a constant current-constant voltage (0.1C cut-off) at a current equivalent to 1.0C to 3.8V, and then discharged at a constant current of 1.0C to 1.5V. This is taken as 1 cycle, and the initial discharge capacity is obtained from the discharge capacity. The cycle is performed again, and the discharge capacity after 300 cycles is measured. The ratio of the discharge capacity after 300 cycles to the initial discharge capacity is obtained and taken as the capacity retention rate (%).

[0158] Capacity retention rate (%) = (Discharge capacity after 300 cycles) ÷ (Initial discharge capacity at 1.0C) × 100 The results are expressed as relative values when the results of Comparative Examples 1, 2, 3, or 4 are set to 1.

[0159] [Gas Generation Amount] The volume of the battery before and after the cyclic implementation was measured by the Archimedes method, and the gas generation amount was calculated by the following formula.

[0160] (Volume after 300 cycles) - (Initial volume) = Gas generation amount (mL) The values of Comparative Examples 1, 2, 3, or 4 were set to 1 for calculation.

[0161] (Measurement of metal precipitation amount) [Amount of Co] The aluminum laminated battery after 300 cycles was disassembled, the negative electrode was taken out, and it was immersed in a 5 wt% nitric acid aqueous solution for 24 hours. After 24 hours, filtration was performed, and the amount of Co (ppm) was calculated for the filtrate by ICP emission spectroscopy.

[0162] (Examples 2 to 35) As shown in Table 1, the type and addition amount of the additive of the non-aqueous electrolyte were changed, and except for this, the non-aqueous electrolyte was prepared in the same manner as in Example 1, and then a battery was fabricated and various evaluations were performed.

[0163] The results are shown in Table 1.

[0164] (Comparative Example 1) An additive was not used, and except for this, the non-aqueous electrolyte was prepared in the same manner as in Example 1, and then a battery was fabricated and various evaluations were performed.

[0165] The results are shown in Table 1.

[0166] [Table 1]

[0167] (Examples 36 to 39) 1,2-Dimethoxyethane (DME) and 1,3-dioxolane (DOL) were mixed so that the volume ratio became 1 / 1, and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) was added to the mixture so that the concentration became 1.0 mol / L to prepare a basic electrolyte.

[0168] As shown in Table 2, the type and addition amount of the additive of the non-aqueous electrolyte were changed, and except for this, the non-aqueous electrolyte was prepared in the same manner as in Example 1, and then a battery was fabricated and various evaluations were performed.

[0169] The results are shown in Table 2.

[0170] (Comparative Example 2) An additive was not used, and except for this, the non-aqueous electrolyte was prepared in the same manner as in Example 36, and then a battery was fabricated and various evaluations were performed.

[0171] The results are shown in Table 2.

[0172] [Table 2]

[0173] (Examples 40 - 43) NaPF6 was added to propylene carbonate (PC) to a concentration of 1.0 mol / L to prepare a basic electrolyte solution.

[0174] As shown in Table 3, the type and amount of the additive in the electrolyte solution were changed. Otherwise, the non-aqueous electrolyte solution was prepared in the same manner as in Example 1, and then a battery was fabricated and various evaluations were performed.

[0175] The results are shown in Table 3.

[0176] (Comparative Example 3) An additive was not used. Otherwise, the non-aqueous electrolyte solution was prepared in the same manner as in Example 40, and then a battery was fabricated and various evaluations were performed.

[0177] The results are shown in Table 3.

[0178] [Table 3]

[0179] (Examples 44 - 47) Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 2 / 98. Sodium bis(trifluoromethanesulfonyl)imide (NaFSI) was added to this mixture to a concentration of 1.0 mol / L to prepare a basic electrolyte solution.

[0180] As shown in Table 4, the type and amount of the additive in the electrolyte solution were changed. Otherwise, the non-aqueous electrolyte solution was prepared in the same manner as in Example 1, and then a battery was fabricated and various evaluations were performed.

[0181] The results are shown in Table 4.

[0182] (Comparative Example 4) An additive was not used. Otherwise, the non-aqueous electrolyte solution was prepared in the same manner as in Example 44, and then a battery was fabricated and various evaluations were performed.

[0183] The results are shown in Table 4.

[0184] [Table 4]

[0185] (Example 48) [Preparation of Electrolyte Solution] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3 / 7. LiPF6 was added to this mixture to a concentration of 1.0 mol / L to prepare a basic electrolyte solution.

[0186] A non-aqueous electrolyte is prepared by adding 0.1 ppm of compound (1-1) to the above basic electrolyte and mixing them.

[0187] [Fabrication of the positive electrode] Add 97 parts by mass of LiNi 0.8 Mn 0.1 Co 0.1 O2 (NMC811), 1.5 parts by mass of acetylene black as a conductive additive, and 1.5 parts by mass of polyvinylidene fluoride (8 mass% NMP solution) as a binder, and mix them using a disperser to form a slurry. The obtained slurry is coated on an aluminum foil with a thickness of 20 μ μm, dried, rolled using a rolling press, and then cut into a shape having a coated portion (positive electrode material layer) with a width of 50 mm and a length of 30 mm and an uncoated portion with a width of 5 mm and a length of 9 mm to fabricate a positive electrode.

[0188] [Fabrication of the negative electrode] Mix 94 parts by mass of silicon oxide powder (SiO) as a negative electrode active material with graphite (mass ratio 10 / 90) and 6 mass% of polyvinylidene fluoride (PVdF) as a binder, and further add N-methyl-2-pyrrolidone (NMP) and mix them to form a slurry. The obtained slurry is coated on a negative electrode current collector including a copper foil with a thickness of 15 μ μm, and dried. It is cut into a specified electrode size and rolled using a roll press to fabricate a negative electrode having a negative electrode material layer formed on the negative electrode current collector.

[0189] [Fabrication of the battery] The fabricated negative electrode having a negative electrode material layer on one side is cut into a shape having a coated portion (negative electrode material layer) with a width of 52 mm and a length of 32 mm and an uncoated portion with a width of 5 mm and a length of 9 mm to fabricate a negative electrode.

[0190] Place the above positive electrode and negative electrode opposite each other with a microporous polyethylene film (separator) having a thickness of 20 μ μm in between, inject the above-obtained non-aqueous electrolyte, and after the non-aqueous electrolyte has fully penetrated into the separator and the like, seal it, pre-charge it, and age it to fabricate an aluminum laminated battery (lithium-ion secondary battery).

[0191] Evaluate the above battery characteristics and the following metal precipitation amount of the obtained battery.

[0192] The results are shown in Table 5.

[0193] [Cycle characteristics] The obtained aluminum laminated battery was charged at a constant current-constant voltage at 25 °C with a current equivalent to 0.2C (hereinafter, referred to as CC / CV charging. ) (0.1C cut-off) up to 4.2V, and then discharged at a constant current of 0.2C to 2.5V. This was regarded as one cycle, and three cycles were carried out. Then, at 45 °C, it was charged at a constant current-constant voltage with a current equivalent to 1.0C (0.1C cut-off) up to 4.2V, and then discharged at a constant current of 1.0C to 2.5V. This was regarded as one cycle, and the initial discharge capacity was determined from the discharge capacity. The cycle was carried out again, and the discharge capacity after 500 cycles was measured. The ratio of the discharge capacity after 500 cycles to the initial discharge capacity was obtained and used as the capacity retention rate (%).

[0194] Capacity retention rate (%) = (Discharge capacity after 500 cycles) ÷ (Initial discharge capacity at 1.0C) × 100 The results were expressed as relative values with the results of Comparative Example 5 or Comparative Example 6 set to 1.

[0195] [Gas volume] The volume of the battery before and after the cycle was measured by the Archimedes method, and the gas generation amount was calculated by the following formula.

[0196] (Volume after 500 cycles) - (Initial volume) = Gas generation amount (mL) Calculated with the value of Comparative Example 5 or Comparative Example 6 set to 1.

[0197] (Measurement of metal precipitation amount) [Mn amount] The aluminum laminated battery after 500 cycles was disassembled, the negative electrode was taken out, and it was immersed in a 5 wt% nitric acid aqueous solution for 24 hours. After 24 hours, it was filtered, and the Mn amount (ppm) in the filtrate was calculated by ICP emission spectrometry.

[0198] (Examples 49 - 82) As shown in Table 5, the type and addition amount of the additive in the non-aqueous electrolyte were changed. Otherwise, it was the same as in Example 48 to prepare a non-aqueous electrolyte, and then a battery was made and various evaluations were carried out.

[0199] The results are shown in Table 5.

[0200] (Comparative Example 5) An additive was not used. Otherwise, it was the same as in Example 48 to prepare a non-aqueous electrolyte, and then a battery was made and various evaluations were carried out.

[0201] The results are shown in Table 5.

[0202] [Table 5]

[0203] (Examples 83 to 86) Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed so that the volume ratio became 2 / 98, and LiN(FSO2)2 (LiFSI) was added to this mixture so as to have a concentration of 1.0 mol / L to prepare a basic electrolyte solution.

[0204] As shown in Table 6, the type and addition amount of the additive in the electrolyte solution were changed. Other than that, the non-aqueous electrolyte solution was prepared in the same manner as in Example 48. In addition, LiNi 0.6 Mn 0.2 Co 0.2 O2 (NMC622) was used as the positive electrode active material. Other than that, the battery was fabricated in the same manner as in Example 48, and various evaluations were performed.

[0205] The results are shown in Table 6.

[0206] (Comparative Example 6) An additive was not used. Other than that, the non-aqueous electrolyte solution was prepared in the same manner as in Example 83. Furthermore, a battery was fabricated and various evaluations were performed.

[0207] The results are shown in Table 6.

[0208] [Table 6]

[0209] As can be seen from the examples in Tables 1 to 6, by using the electrolyte solution obtained in the examples, the cycle characteristics of the secondary battery are improved, and the amount of gas generation and metal precipitation during cycling are reduced.

[0210] Industrial Applicability Electrochemical devices such as secondary batteries using the electrolyte solution of the present invention can be used as various power sources such as mobile power sources and automotive power sources.

Claims

1. An electrolyte, characterized in that, containing at least one compound represented by the following general formula (1): Rf 1 OR (1) In formula (1), Rf 1 is a fluoroalkyl group having 1 to 5 carbon atoms, and R is K or Na.

2. The electrolyte according to claim 1, wherein, The Rf of the compound represented by the general formula (1) 1 is any one of the following formulas (1a) to (1e): (1a) CF2HCF2 (1b) CF2HCF2CH2 (1c) CF3CHFCF2 (1d) CF3CF2CH2 (1e) CF2HCF2CF2CF2CH2.

3. The electrolyte according to claim 1 or 2, wherein The content of the compound represented by the general formula (1) is 0.01 ppm to 10,000 ppm relative to the whole electrolyte.

4. The electrolyte according to any one of claims 1 to 3, wherein The electrolyte further contains a compound represented by the following general formula (2): Rf 2 ORf 3 (2) In formula (2), Rf 2 and Rf 3 are each independently a fluoroalkyl group having 1 to 8 carbon atoms.

5. The electrolyte according to claim 4, wherein, The compound represented by the general formula (2) is at least one selected from CF2HCF2CH2OCF2CF2H, CF2HCF2CH2OCF2CHFCF3, and CF3CF2CH2OCF2CF2H.

6. The electrolyte according to claim 4 or 5, wherein The content of the compound represented by the general formula (2) is 0.1 to 90% by mass relative to the whole electrolyte.

7. The electrolyte according to any one of claims 4 to 6, wherein, The content of the compound represented by the general formula (1) is 0.0000001 to 10% by mass relative to the compound represented by the general formula (2).

8. The electrolyte according to any one of claims 4 to 7, wherein The content of the compound represented by the general formula (2) is 0.1 to 75% by mass relative to the whole electrolyte, and the content of the compound represented by the general formula (1) is 0.001 to 5% by mass relative to the compound represented by the general formula (2).

9. The electrolyte according to any one of claims 1 to 8, wherein, The compound represented by the general formula (1) is CF2HCF2CH2ONa.

10. The electrolyte according to any one of claims 4 to 9, wherein, The compound represented by the general formula (2) is CF2HCF2CH2OCF2CF2H.

11. An electrochemical device, characterized in that, An electrolyte according to any one of claims 1 to 10 is provided.

12. A secondary battery, characterized in that, An electrolyte according to any one of claims 1 to 10 is provided.

13. A sodium-ion secondary battery, characterized in that, An electrolyte according to any one of claims 1 to 10 is provided.

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